Ship s propeller



(No Model.)

A. T. ELFORD. SHIPS PROPEL'LER.

No. 495,727. Patented Apr. 18; 1893.

UNITED STATES PATENT OFFICE.

ALFRED T. ELFORD, OF SAN FRANCISCO, CALIFORNIA.

SHIPS PROPELLER.

SPECIFICATION forming part of Letters Patent No. 495,727, dated April 18, 1893.

Application filed August 22, 1892. Serial No. 443,716. (No model.)

T or whom it may concern.-

Be it known that I, ALFRED T. ELFORD, a citizen of the United States, residing at the city and county of San Francisco, State of California, have invented certain new and useful Improvements in Ships Propellers, of which the following is a specification.

My invention relates to that class of propellers connected to an axis or axle parallel with the keel of the vessel and revolving beneath the surface of the water at the stern of the vessel. 7

The object of my invention is to produce a propeller wherein the vibration slip and friction is considerably reduced and the actual advance or rate of the ship augmented.

The improvements constituting my said invention comprise a novel construction and arrangement of blades connected to arms spirally arranged around a common axis or hub suitably sustained by annular bands so that each blade forming the screw will stand perpendicular to the axis of the hub and cross the same diagonally at an angle of about forty-five degrees.

The accompanying drawings which form part of this specification are referred to therein by figures and letters,and representa propeller constructed according to my invention.

Figurel is a front elevation. Fig. 2 is a side view. Fig. 3 is a side view of one of the blades and Fig. 4 a cross section.

The hubAof my propeller is cast solid with the exception of the usual pipe, slots for feathers, and bolt-holes for keying to the driving shaft, and a series of arms B, B, B, are arranged spirally from front to rear around the hub, the radii of which form the diameter of a true circle in each series. The first of the arms, 1, in each series stands at a true tangent to the hub; the third, 3, is truly radial thereto; and the second, 2, is located at about midway between the first and thirdall as seen in Fig. 1. Taken diagonally across or spirally around the hub, the ends of each series form a support for the diagonal blades of the propeller. Each of the spirally arranged arms B, B, passes through a circular collar or band C, C, C, before entering the blades and thus the arms are strengthened and much vibration prevented, each band being independent of the other. By arranging the first of the series of arms B at a tangent to the hub A, it will be seen that when the latter revolves this arm is drawn forward, and

the resistance of the water against the blade is more strongly overcome than if the arm were truly radial to the hub. At the same time, by having the other arms 2 and 3 respectively truly and nearly radial to the hub, the tendency of the first arm 1 toincline to the rear is resisted; and the tendency of the outer ends of all the arms to press inward toward the hub, is overcome by the band C which holds such outer ends always at the same distance from the hub. The blades'D, D, are set at an angle about forty-five degrees with the longitudinal axis of the hub perpendicular and spirally to it, by which a screw is formed in segments that will be free from back-flow or dead-water. The edges and ends of each blade are gothic in form or oval with a sharp line drawn in the center of the oval. from all points so as to be in cross section nearly like an ellipse bisected on its shorter diameterpracticallyasection of half a conoid, and such edges and ends are then smoothly finished to present as little friction to the water as possible and each blade is slightly arched as at D and the spokes or arms bands and blades are set and arranged in a true geometrical order to give the greatest rate and the least possible slip. As thus constructed it will be seen that in operation the forward and backward thrust of the propeller will be the same.

Having thus described my invention, what I claim, and desire to secure by Letters Patcut, is-

The herein described propeller comprising a hub A, a number of series of arms seated therein, each series having three arms arranged at dilferent circles around the length of the hub, the first of the series standing at a tangent to the hub, the third truly radial thereto, and the second at an angle between the other two, a band C surrounding the hub in a plane with each of said circles and through which band said arms pass, and a blade D secured to the outer ends of the arms of each series, set spirally around the hub and having its edges and ends conoidal in cross section, as and for the purpose set forth.

In testimony that I claim the foregoing I have hereunto set my hand and seal.

ALFRED T. ELFORD. [L.S.] 

